diff --git a/qt/scientific_interfaces/Indirect/ISISEnergyTransfer.cpp b/qt/scientific_interfaces/Indirect/ISISEnergyTransfer.cpp
index e5dcc0f780dab0489690d9e2fb592afbd474bdcc..6d2d43b6084c6c0a1c34ffcf776f955abcac31a1 100644
--- a/qt/scientific_interfaces/Indirect/ISISEnergyTransfer.cpp
+++ b/qt/scientific_interfaces/Indirect/ISISEnergyTransfer.cpp
@@ -43,7 +43,7 @@ std::string createDetectorGroupingString(std::size_t numberOfDetectors,
                                          std::size_t numberOfGroups) {
   const auto groupSize = numberOfDetectors / numberOfGroups;
   if (groupSize == 0)
-    return createRangeString(0, numberOfDetectors);
+    return createRangeString(0, numberOfDetectors - 1);
   return createDetectorGroupingString(groupSize, numberOfGroups,
                                       numberOfDetectors);
 }